Weston Volunteer Fire Brigade chief fire officer Bevan Koppert said about 11.30pm crews were called to a flooded unoccupied newly built house in Grove Ave by concerned neighbours.
They later "accidentally" discovered the large hole in nearby Westview Dr when they went to investigate the cause of the flooding.
"Two houses were being threatened," Mr Koppert said.
"We put in two portable pumps and pumped for four to five hours to keep the water out of the second house.
"They went to check if the water was coming out of the culvert, it seemed to be building up too quick . . . and that's when they found the culvert had collapsed . . . or whatever it did."
About eight firefighters, including the Waitaki Rural Fire Force who joined the effort later, pumped water until the rain stopped.
Waitaki District Council assets group manager Neil Jorgensen said he could not yet say whether the culvert had become blocked or partially collapsed.
He could not say at this point when the road would re-open.
Mr Jorgensen praised the "great" work of the fire crews.
The Weston Volunteer Fire Brigade had responded to about seven call outs since the rain began, including a flooded section this morning about 10.45am, Mr Koppert said.
